Disc Brake of Hydraulic Self-Energizing Design with Adjusting Device

ABSTRACT

A self-energizing disc brake includes a brake-internal hydraulic arrangement with a supply circuit and an expansion vessel, a brake application device with a brake application cylinder for applying a brake pad in the direction of a brake disc, a force transmission unit which supports the brake pad at a wedge angle on the brake application device, a tangential-force absorbing cylinder for switching over the wedge angle and being operatively connected to the force transmission unit; an electric-motor actuator which acts on the brake application device via the hydraulic arrangement, a distributor cylinder arranged in series between the electric-motor actuator and the brake application device for pressure boosting, and a control unit for controlling switchover of the wedge angle between the tangential-force absorbing cylinder and the electric-motor actuator. An adjusting device adjusts brake pad wear, and has a movable screw spindle, which is operatively connected to the brake application device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT International Application No.PCT/EP2011/059822, filed Jun. 14, 2011, which claims priority under 35U.S.C. §119 from German Patent Application No. DE 10 2010 024 076.1,filed Jun. 17, 2010, the entire disclosures of which are hereinexpressly incorporated by reference.

This application contains subject matter related to U.S. applicationSer. No. ______, entitled “Disc Brake of Hydraulic Self-EnergizingDesign With Parking Brake Device,” and application Ser. No. ______,entitled “Disc Brake of Hydraulic Self-Energizing Design With ForceTransmission Unit,” both filed on even date herewith.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a disc brake of hydraulic self-energizingdesign with a readjustment device.

A disc brake with an electromotive actuator of self-energizing designand with a brake-internal hydraulic arrangement is described in theapplicant's application WO 2007/045430 A1.

A readjustment device of a disc brake of the type is composed of arelatively large number of parts.

It is the object of the present invention to improve a readjustmentdevice of a generic disc brake.

It is thereby possible to realize a wear-compensating readjustment whichpermits the construction of a compact disc brake with a smaller numberof parts than in the prior art.

According to the invention, the disc brake is provided with areadjustment device for readjustment to compensate brake pad wear,wherein the readjustment device has an adjustable screw spindle whichserves, in operative connection with the brake-application device, forgenerating a follow-up movement of the at least one brake pad. Here, thescrew spindle is integrated in a particularly space-saving manner intothe at least one brake-application cylinder. The screw spindle canfurthermore be coupled to the electromotive actuator in order to bedriven, and has a readjustment piston which can be hydraulicallyadjusted in the tangential force absorption cylinder during a follow-upmovement of the at least one brake pad.

Functional reliability of wedge angle switching and pressure boosting isthus also permitted in a simple manner.

A disc brake of self-energizing construction comprises the following: abrake-internal hydraulic arrangement with a reservoir circuit and anexpansion vessel; a brake-application device having at least onebrake-application cylinder for the brake-application movement of atleast one brake pad in the direction of a brake disc; at least one forcetransmission unit which supports the at least one brake pad on thebrake-application device at a wedge angle; at least one tangential forceabsorption cylinder for wedge angle switching, which tangential forceabsorption cylinder is operatively connected to the at least one forcetransmission unit; an electromotive actuator which acts on thebrake-application device via the hydraulic arrangement; a distributorcylinder for pressure boosting, which distributor cylinder is arrangedin series between the electromotive actuator and the brake-applicationdevice; and a control unit which is provided for controlling the wedgeangle switching between the tangential force absorption cylinder and theelectromotive actuator, wherein the disc brake comprises a readjustmentdevice for readjustment to compensate brake pad wear, wherein thereadjustment device has an adjustable screw spindle, which isoperatively connected to the brake-application device for the purpose ofgenerating a follow-up movement of the at least one brake pad and can becoupled to the electromotive actuator in order to be driven, and areadjustment piston, which can be hydraulically adjusted in thetangential force absorption cylinder during a follow-up movement of theat least one brake pad.

It is thus possible, likewise in a space-saving manner, for areadjustment drive wheel with a shaft drive wheel coupled to the screwspindle to be designed as a hydraulic gear motor, which can behydraulically coupled to the electromotive actuator by way of ahydraulic switch. The hydraulic switch can preferably be controlled bythe control unit.

A great advantage is that the drive of the readjustment device isrealized hydraulically. The gear motor can be of flat construction, andthe hydraulic lines can be integrated into the housing.

It can also be made possible in this way for the readjustment piston tobe connectable, for a follow-up movement, to the reservoir circuit byway of a directional valve.

In a preferred embodiment, it is provided that the expansion vessel ofthe reservoir circuit of the brake-internal hydraulic arrangement isequipped with a sensor for detecting pad wear, wherein the sensor isconnected to a brake control unit which, for the activation of thereadjustment device for a corresponding follow-up movement of the atleast one brake pad, is coupled at least to the electromotive actuatorand to the control unit. A brake control unit of this type is providedin a brake of this type in any case, and can be upgraded withcorresponding software in a simple manner. An auxiliary unit mayself-evidently also be provided. The sensor for the liquid level in theexpansion vessel may thus be used as a travel sensor for measurement ofthe horizontal adjustment of the brake pads, detection of hydraulicfluid losses, and determination of the brake pad wear status. Instead ofa travel sensor, use may also be made, as an inexpensive alternative, ofa pressure sensor to detect the present oil quantity in the expansionvessel.

In a preferred embodiment, the control unit may have a control discwhich can be driven hydraulically, by way of a control drive in the formof a hydraulic gear motor, by the electromotive actuator via a switchingvalve. It is possible in this way, by way of simple control means, forthe electromotive actuator to be used as a drive for different tasks. Inthis case, the electromotive actuator, in addition to its function as apressure generator for the brake-application device, acts as a drivesource for the readjustment device and the control device.

The readjustment device may be provided with an emergency releasedevice, which is preferably coupled to the readjustment drive wheel. Inthis way, not only is a manual release of the brake possible in theevent of an emergency, but a resetting of the brake-application deviceis also possible for example in the event of a pad change.

The follow-up movement of the brake pads in the event of wear may takeplace after a certain number of braking operations. In the simplestcase, the readjustment takes place at the end of every actuation of theparking brake, because here, the air play between the mechanicalabutment of the screw spindle wheel against the cylinder base and thecontact point of the brake pads with the disc must be newly set in anycase.

In normal, unbraked driving operation for an intelligent follow-upmovement in the event of wear of the brake pads (and also of the brakedisc), it is alternatively possible for the readjustment device to beequipped with at least one sensor. The sensor may detect a readjustmenttravel in order to determine a present follow-up movement, and transmitthe readjustment travel to the brake control unit for the regulation ofthe readjustment device. The brake control unit can, in a conventionalmanner, compare the present travel with a comparison value stored forexample in a table, and thus always set the brake pad with its requiredair play.

For this purpose, the sensor for determining a readjustment travel maybe a multi-turn potentiometer which is directly or indirectly coupled tothe screw spindle. Such angle sensors are available in a variety ofembodiments for numerous purposes and in high quality, even for hightemperatures such as may arise in a brake.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of one ormore preferred embodiments when considered in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a first exemplary embodiment of adisc brake according to the invention;

FIG. 2 is a schematic, partially sectional illustration of a secondexemplary embodiment of the disc brake according to the invention in anormal position;

FIG. 3 is a schematic, partially sectional illustration of the secondexemplary embodiment as per FIG. 2 in a position of maximum brakeapplication;

FIG. 4 is a schematic, partially sectional illustration of the secondexemplary embodiment as per FIG. 2 in a normal position with maximumbrake wear;

FIG. 5 shows a schematic, perspective view of the second exemplaryembodiment as per FIG. 2; and

FIG. 6 shows a schematic, perspective view of a detail from FIG. 5.

DETAILED DESCRIPTION OF THE DRAWINGS

Components of identical or similar function are denoted by the samereference numerals unless stated otherwise.

Here, the expression “oil” refers to hydraulic fluid.

FIG. 1 is a schematic illustration of a first exemplary embodiment of adisc brake 1 according to the invention. FIG. 1 will be described inconjunction with FIG. 2 and FIG. 3. FIG. 2 is a schematic, partiallysectional illustration of a second exemplary embodiment of the discbrake according to the invention in a normal position, and FIG. 3 is aschematic, partially sectional illustration of the second exemplaryembodiment as per FIG. 2 in a position of maximum brake application.

The disc brake 1 has a brake caliper 40 which engages over a brake disc2. At both sides of the brake disc 2 there is arranged in each case onebrake pad 3, 3′ with brake pad carrier 4, wherein the brake pad 3′ shownat the bottom in FIG. 2 (and not illustrated in FIG. 1) bears againstthe brake caliper 40, and the other brake pad 3 is operatively connectedto a brake-application device. The axis of the brake disc 2 is not shownand runs, as is easily conceivable, vertically upward below the plane ofthe drawing. A forward movement of a vehicle to which the disc brake 1is assigned is intended to run from right to left in FIGS. 1 to 3,wherein the brake disc 2 then rotates counterclockwise.

Here, the pad carrier 4 is formed with two wedge-shaped support devices5, wherein the support devices are supported at a wedge angle on thebrake-application device, with which the support devices are operativelyconnected in each case by a force transmission unit 7 to in each caseone brake-application element 9. The brake-application elements 9 areconnected at their top end in each case to a brake-application piston 10of a brake-application cylinder 11. The brake-application cylinders 11are arranged adjacent to one another such that the brake pads 3, 3′ canbe pressed uniformly against the brake disc 2 during a brakeapplication.

A screw spindle 12 with a thread is screwed into the brake-applicationpiston 10 in each case in the longitudinal direction. The screw spindles12 are each provided, on the top ends thereof, with a screw spindlewheel 13, wherein each screw spindle wheel 13 engages with areadjustment pinion 14. The readjustment pinions 14 are in each caserotationally conjointly connected by way of readjustment shafts 15 toreadjustment shaft wheels 16, which jointly engage with a readjustmentdrive wheel 17. The readjustment drive wheel 17 is formed, for example,as a hydraulically operated gear motor 19, and in this case are equippedwith an emergency release device 18 which can be adjusted for example byuse of a tool in order to actuate the readjustment drive wheel 17. Thereadjustment wheels 13, 14, 16 and 17 have toothings, for example, andare used for wear-compensating readjustment of the brake pads 3, 3′, aswill be explained in more detail further below. The readjustment wheels13, 14, 16 and 17, the emergency release device 18, the readjustmentshafts 15 and the gear motor 19 form, together with the screw spindles12, a readjustment device 20 of the disc brake 1.

Return springs 12 a are arranged in each case between the brake caliper40 and screw spindles 12 in the longitudinal direction of the screwspindles 12 and, in the normal position shown in FIG. 2, pull the brakepad 3, 3′ back away from the brake disc 2 to generate a certainso-called air play. Further springs (not illustrated) are provided forholding the brake-application piston 10 and brake pad 3 together.

The force transmission units 7 have in each case a diverting lever 6,wherein the diverting levers 6 are situated opposite one another andthrust portions 8 are operatively connected to a plunger 23 of atangential force absorption cylinder 21. Here, the plunger 23 is part ofa stepped absorption piston 22 which, together with the tangential forceabsorption cylinder 21, defines first to third pressure chambers 24, 25and 26.

The pressure chambers 24, 25 and 26 are connected in each case viaintermediate lines 55 to a control unit 27, which is a constituent partof a hydraulic system of the disc brake 1. The hydraulic system will nowbe explained in more detail on the basis of FIG. 1.

An electromotive actuator 30, for example an electric motor with agearwheel pump, is connected to a reservoir circuit 46 via a pumpsuction line 50 with a suction valve 39, for example a directionalvalve. The reservoir circuit 46 is hydraulically connected at one sideto an expansion vessel 36 and to a first pressure sensor 41. At theother side, the reservoir circuit 46 can be connected by way of arelease valve 37 to a pump pressure line 51 of the electromotiveactuator 30. Furthermore, the reservoir circuit 46 is connected to thecontrol unit 27 and to an admission pressure chamber 33 of a distributorcylinder 31.

The reservoir circuit 46 is, for example, charged with a reservoirpressure of approximately 1 to 4 bar. A pressure sensor 41 measures thetravel-dependent change in pressure owing to the spring stiffness of acompression spring mounted above a piston. Here, the piston shouldexhibit low sliding and static friction. By detecting thetravel-direction-dependent pressure signal hysteresis, the slidingfriction can be detected and substantially compensated by way ofevaluation software in the control unit.

The electromotive actuator 30 is furthermore connected via the pumppressure line 51 to an inlet pressure chamber 35 of the distributorcylinder 31 and to a hydraulic switch 44. Also connected to the pumppressure line 51 is a control drive pressure line 49 which leads to acontrol drive 28 of the control unit 27. A control drive return line 48is connected between the control drive 28 and a position b of aswitching valve 38. Here, a closed position a of the switching valve 38connects the pump suction line 50 to an intermediate circuit 47 which isconnected firstly to the control unit 27 via connecting lines 56.Furthermore, the intermediate circuit 47 is connected to the gear motor19 of the readjustment device 20, wherein a gear motor pressure line 52connects the gear motor 19 at the pressure side to the hydraulic switch44. The hydraulic switch 44 is furthermore connected via a hydraulicswitch control line 53 to the control unit 27.

The control unit 27 is, for example, a plate-like, rotatable controldisc with control bores which perform different functions of the discbrake 1 in different operating states and perform control tasks. Thecontrol disc is for example coupled to a hydraulic gear motor as controldrive 28. The control disc is also operatively connected to a controltransmitter 29. A superordinate, for example electronic brake controlunit (not shown) controls and regulates the braking processes and statesof the disc brake 1. For this purpose, the brake control unit controlsthe valves 37 and 38, which are for example electromagnetic valves, andthe electromotive actuator 30. The control unit also communicates withthe first pressure sensor 41 and with further pressure sensors, of whicha second pressure sensor 42 determines a pressure in the intermediatecircuit 46. A third pressure sensor 43 serves for determining a pressurein the pump pressure line 51, wherein the pressure may be up to 130 bar.

The distributor cylinder 31 has a stepped piston 32 for pressureboosting, synchronization and uniform loading of the brake-applicationcylinder 11 with a brake-application pressure of up to approximately 250bar. For this purpose, the stepped piston 32 forms, together with thebrake-application cylinder 11, high-pressure chambers 34, 34′, which areconnected in each case via a high-pressure line 54 to thebrake-application cylinders 11.

The disc brake 1 is a hydraulic, self-energizing disc brake, thefunction of which will now be explained.

Upon the start of a braking operation, hydraulic fluid is sucked out ofthe reservoir circuit 46 and out of the expansion vessel 36 via thesuction valve 39 by way of the electromotive actuator 30. Here, theelectromotive actuator 30 increases the pressure in the pump pressureline 51, as a result of which the stepped piston 32 of the distributorcylinder 31 is adjusted and the brake-application cylinder 11 is chargedwith pressure. The brake pads 3, 3′ are thus pressed against the brakedisc 2 until a self-energizing process is initiated.

Here, the brake pad 3 is displaced to the left in FIG. 3, against a stopof the brake caliper 40, owing to friction. The left-hand forcetransmission unit 7, as diverting lever 6, is pivoted downward, and theright-hand force transmission unit 7, as further diverting lever 6, ispivoted upward. The diverting levers 6 are pivoted by the tangentialforce thus generated. The right-hand diverting lever 6 diverts thetangential force into a vertical force which is transmitted, via thethrust portion 8 of the diverting lever, to the plunger 23 of thetangential force absorption cylinder 21. Here, a thrust plate 23 aserves for a uniform and low-friction transmission of force. Furtherbraking forces are introduced into the brake caliper 40 by way of thebrake-application cylinders 11 via the force transmission unit 7, inthis case that on the right-hand side. On the left-hand side, thediverting lever 6, by way of its portion arranged between thebrake-application element 9 and the support device 5, transmits thebrake-application force of the left-hand brake-application cylinder 11.On the right-hand side, the transmission of the brake-application forceof the right-hand brake-application cylinder 11 is performed by ashoulder element 60 of the right-hand force transmission unit 7. If thevehicle (not shown) travels backward, the above-described process isreversed, as is easily comprehensible, and the left-hand diverting lever6 transmits the tangential force to the tangential force absorptioncylinder 21.

When the distributor piston 32 is in the rest position (at the left-handstop in the drawing), the two high-pressure chambers 34, 34′ areconnected to the admission pressure chamber 33. In this way, the twobrake-application pistons 10 can be hydraulically newly balanced intheir rest position (pulled back against the stop). At the same time,this serves to return excess oil from the brake-application cylinders 11during the pad change, when the brake-application pistons 10 are fullyretracted again.

Here, the control disc of the control unit 27 is set by way of thecontrol drive 28 such that the pressure chambers 24, 25 and 26 of thetangential force absorption cylinder 21 can be connected in sevendifferent combinations either to the reservoir circuit 46 and/or to theintermediate circuit 47, which is connected by way of the switchingvalve 38 to the pump suction line 50. It is thus possible for the discbrake 1 to be adapted to a present friction coefficient. Differentso-called wedge angles can be set. Measurement values for thedetermination of the present friction coefficient are provided by thepressure sensors 41, 42, 43 and further parameters, for example from avehicle controller. The tangential force absorption cylinder 21 thusdelivers a pressure which, to boost the pressure in the pump pressureline 50, acts on the brake-application cylinder 11 via the distributorcylinder 31 and reduces the pumping power of the electromotive actuator30. The distributor cylinder 31 may, together with the twobrake-application cylinders 11, synchronize the brake-applicationmovement thereof, compensate oblique wear of the brake pads 3, 3′, andlower a pressure level between the tangential absorption cylinder 21 andthe distributor cylinder 31 in the intermediate circuit 46. Here, thedistributor cylinder 31 serves as a pressure booster for thebrake-application cylinder 11.

At the end of the braking process, the electromotive actuator 30 isdeactivated, and the release valve 37 is activated. As a result, thepressure in the pump pressure line 51 is dissipated, wherein withfalling brake-application pressure in the brake-application cylinders11, the return springs 12 a return the brake pad 3 again into its normalposition with air play.

The release valve 37 may also be used, in the event of a fault, as anemergency release valve for releasing the disc brake 1. The releasevalve is for example a magnetic valve which is open in the deenergizedstate.

The expansion vessel 36 furthermore serves for receiving the volumes ofthe pressure chambers 24, 25, 26, which are connected to the reservoircircuit 46 by way of the control unit 27, of the tangential forceabsorption cylinder 21. The expansion vessel 36 also has sensors fordetermining hydraulic fluid losses. The pad wear of the brake pads 3, 3′can also be measured in this way.

In the event of wear being detected in this way, at a certain wearvalue, the switching valve 38 is switched by the brake control unit intoposition b, and the electromotive actuator 30 is activated. Here, thecontrol drive return line 48 is connected to the pump suction line 50,and the hydraulic gear motor 28 of the control unit 27 adjusts thecontrol disc such that, via the hydraulic switch control line 53, aslide 45 of the hydraulic switch 44 is displaced into an open position,for example by the pressure, acting on the hydraulic switch, of the pumppressure line 51 connected to the hydraulic switch. The open position ofthe slide 45 then connects the pump pressure line 51 to the gear motorpressure line 52 and exerts the pressure on the gear motor 19 of thereadjustment device 20. The readjustment drive wheel 17 thus rotates thescrew spindles 12 via the gearwheels 16, 14, 13, whereby thebrake-application elements 9 of the brake-application cylinders 11 areadjusted in the direction of the brake disc 2 and readjust thedetermined wear travel of the brake pad 3 or 3′ until the air play ofthe normal state is re-established. Various sensors, for example anglesensors on the gear motor 19, may serve for the precise measurement ofthe readjustment travel. The sensor may for example be a multi-turnpotentiometer, the electrical resistance of which varies proportionallywith respect to the readjustment travel over a rotational angle which isproportional to the readjustment travel, and thus provides a measure forthe readjustment travel.

The readjustment process is ended, when the normal air play is reached,in that, by way of the switching valve 38, the control drive 28 isactuated for the deactivation of the hydraulic switch 44 via thehydraulic switch control line 53, as a result of which the gear motor 19is deactivated, and then the electromotive actuator 30 is deactivated.

FIG. 4 is a schematic, partially sectional illustration of the secondexemplary embodiment as per FIG. 2 in a normal position with maximumbrake wear of the brake pads 3, 3′. It can be clearly seen that thebrake-application pistons 10 have been adjusted in the brake-applicationcylinders 11 downward in the direction of the brake disc 2 by thescrewed-out screw spindles 12. Here, brake-application pressure chambers57 of the brake-application cylinders 11 are subsequently filled withhydraulic fluid in order to compensate the readjustment travel. This maytake place by use of the reservoir circuit 46. Furthermore, thewear-compensating readjustment of the brake pad 3 has the result thatthe diverting levers 6 are likewise adjusted, with their thrust portions8, by the readjustment travel. Without compensation of the readjustmenttravel, a function of the tangential force absorption cylinder 21 wouldnot be possible over the entire readjustment travel. For this purpose,the stepped absorption piston 22 of the tangential force absorptioncylinder 21 is provided with a readjustment piston 23 b, which isarranged, between the plunger 23 and the stepped absorption piston 22,in the stepped absorption piston so as to be displaceable coaxially withrespect thereto. The readjustment piston 23 b is situated in the steppedabsorption piston 22 and forms with the latter a readjustment chamber58, which communicates via a directional valve 59 with the thirdpressure chamber 26 of the tangential force absorption cylinder 21.

The readjustment of the readjustment piston 23 b likewise takes place byuse of the reservoir circuit 46, in that the pressure chambers 24 to 26are filled from the reservoir circuit 46 by way of the control unit 27.Here, the readjustment chamber 58 is also filled via the directionalvalve 59. The pressure in the reservoir circuit 46 must be adequate forthis purpose. The pressure may, however, also be increased by way ofadditional pressure-increasing measures by use of the electromotiveactuator 30 using additional valves and regulating means, wherein thereadjustment travel of the readjustment piston 23 b may be detected byuse of suitable sensors. If force is now introduced into thereadjustment piston 23 b via the plunger 23 during a braking process,the hydraulic fluid in the readjustment chamber 58 cannot escape owingto the directional valve 59. In the event of a pad change and resettingof the readjustment device 20, the readjustment chamber 58 is likewiseevacuated, which may be realized for example by opening the directionalvalve 59 or by way of a pin positioned centrally in the base of thepressure chamber 26. This will be explained below.

A readjustment of the pad wear takes place in each case after therelease of the immobilizing brake or parking brake. The working chamberof the cylinder of the stepped absorption piston 22, that is to say thepressure chambers 24, 25 and 26, permits a slightly greater movementtravel than the diverting levers 6 require at their maximum deflection.

The readjustment pistons 23 b can thus adjust themselves automatically.To deploy the piston 23 b, additional oil is admitted through thedirectional valve 59 as backflow preventer into the cylinder chamber(readjustment chamber 58) above the readjustment piston 23 b. Thisoccurs when, by way of spindles 12, the brake-application pistons 10have been adjusted further in the direction of the brake disc 2 (owingto pad wear) after the end of the parking brake or handbrake actuation.The stepped absorption piston 22 thereby abuts against its outermovement stop. The hydraulic pressure in the readjustment piston 23 b,that is to say in the readjustment chamber 58, falls, such that thedirectional valve 59 opens and oil flows into the readjustment chamber58.

The reversed retraction of the readjustment piston 23 b takes placeduring an exchange of the brake pads 3, 3′ and/or of the brake disc 2.For this purpose, the spindles 12 are hydraulically actuated by the gearmotor 19 such that the brake-application pistons 10 are retracted. Thestepped absorption piston 22 is thereby also retracted. The hydraulicoil above the brake-application pistons 10 and above the steppedabsorption piston 22 is forced into the expansion vessel 36. Here, thestepped absorption piston 22 is retracted until the piston base surfacethereof makes contact with the cylinder chamber base of the thirdpressure chamber 26. Shortly before the contact point, a pin (notillustrated but easily conceivable) which is positioned centrally in thebase of the third pressure chamber 26 presses against the directionalvalve 59, such that the latter opens and the oil situated in thereadjustment chamber 58 is forced via the third pressure chamber 26 intothe expansion vessel 36. Position regulation for the stepped absorptionpiston 22 is thus realized in a simple manner, such that the steppedabsorption piston, despite occasional pad wear-compensatingreadjustment, can follow the movement profile of the diverting lever 6without being hindered by its mechanical stops.

FIG. 5 shows a schematic perspective view of the second exemplaryembodiment as per FIG. 2, and FIG. 6 shows a schematic perspective viewof a detail from FIG. 5.

FIG. 5 shows a portion of a brake caliper 40 in which, in this case, allof the hydraulic components are arranged. Between the brake-applicationcylinders 11, of which in this case the upper ends of the screw spindles12 with the return springs 12 a are visible, the tangential forceabsorption cylinder 21 and the distributor cylinder 31 are arranged onebehind the other, wherein the cylinders 11, 21 and 13 are substantiallyall situated parallel to one another. In the lower region, illustratedfrom another perspective in FIG. 6, a stop element 40 a is arranged,between the brake caliper 40 and pad carrier 4, below the tangentialforce absorption cylinder 21. Adjacent to the stop element 40 a, theremay also be positioned on the inner side a spring for holding thebrake-application piston 10 and brake pad 3 together. The brake pad 3 isof circular-arc-shaped form corresponding to the brake disc 2, whereinthe diverting levers 6 with the shoulder elements 60 are arrangedbetween piston elements 9 and the support device 5, and the thrustportions 8 point radially outward and bear against the thrust plate 23a.

The disc brake 1 according to the invention thus has the followingcharacteristics and advantages:

-   -   High energy density and force density (180 kN brake-application        force can be realized in the structural space);    -   Automatic self-energization in both directions of travel    -   Automatic and reliable emergency release function as a result of        a normally-open magnetic valve (release valve 37);    -   Electromotive drive;    -   Hydraulic force transmission by use of brake or hydraulic fluid;    -   Hydraulic components are a reliable and known standard        technology;    -   Shorter braking travel as a result of improved ABS regulation        (small masses to be accelerated);    -   Short response and adjustment time (small masses to be        accelerated);    -   Intelligent wear-compensating readjustment for rear-side pads        without additional motor;    -   Low electrical actuation power (for example approximately 60 W        to a maximum of 150 W);    -   Inexpensive gearwheel pump instead of expensive mechanical        heavy-duty gearing;    -   One electric motor drives, via the gearwheel pump, the brake        application, the control unit (valve disc), the readjustment        device (pad wear), and the parking brake;    -   Simple and precise force measurement by use of pressure sensors;    -   Compact, lightweight design, low sensitivity with respect to        vibrations;    -   Good sliding and lubricating properties of the components as a        result of the use of oil;    -   Robust regulation as a result of being free from play, no        mechanical gearwheel pairings for braking force transmission;    -   For example, a four-stage switching means permits 16 different        wedge angles;    -   Direct measurement of the brake-application force and of the        braking force possible;    -   Precise measurement or detection of the contact point/biting        point of the brake pads by differential pressure measurement;    -   Measurement of the pad wear possible without additional wear        travel sensors.

Even though the present invention has been described above on the basisof preferred exemplary embodiments, it is not restricted thereto, butrather may be modified in a variety of ways. The tangential forceabsorption cylinder 21 may have more or fewer pressure chambers 24 to26. The control unit 27 may also have magnetic valves instead of or inaddition to a control disc.

List of Reference Numerals

1 Disc brake

2 Brake disc

3, 3′ Brake pad

4 Pad carrier

5 Support device

6 Diverting lever

7 Force transmission unit

8 Thrust portion

9 Brake-application element

10 Brake-application piston

11 Brake-application cylinder

12 Screw spindle

12 a Return spring

13 Screw spindle wheel

14 Readjustment pinion

15 Readjustment shaft

16 Readjustment shaft wheel

17 Readjustment drive wheel

18 Emergency release device

19 Gear motor

20 Readjustment device

21 Tangential force absorption cylinder

22 Stepped absorption piston

23 Plunger

23 a Thrust plate

23 b Readjustment piston

24 First pressure chamber

25 Second pressure chamber

26 Third pressure chamber

27 Control unit

28 Control drive

29 Control transmitter

30 Pump

31 Distributor cylinder

32 Stepped piston

33 Admission pressure chamber

34, 34′ High-pressure chamber

35 Inlet pressure chamber

36 Expansion vessel

37 Release valve

38 Switching valve

39 Suction valve

40 Brake caliper

40 a Stop element

41 First pressure sensor

42 Second pressure sensor

43 Third pressure sensor

44 Hydraulic switch

45 Slide

46 Reservoir circuit

47 Intermediate circuit

48 Control drive return line

49 Control drive pressure line

50 Pump suction line

51 Pump pressure line

52 Gear motor pressure line

53 Hydraulic switch control line

54 High-pressure line

55 Intermediate lines

56 Connecting lines

57 Brake-application pressure chamber

58 Readjustment chamber

59 Directional valve

60 Shoulder element

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

What is claimed is:
 1. A self-energizing disc brake, comprising: abrake-internal hydraulic arrangement with a reservoir circuit and anexpansion vessel; a brake-application device having at least onebrake-application cylinder for the brake-application movement of atleast one brake pad in the direction of a brake disc; at least one forcetransmission unit which supports the at least one brake pad on thebrake-application device at a wedge angle; at least one tangential forceabsorption cylinder for wedge angle switching, which tangential forceabsorption cylinder is operatively connected to the at least one forcetransmission unit; an electromotive actuator which acts on thebrake-application device via the hydraulic arrangement; a distributorcylinder for pressure boosting, which distributor cylinder is arrangedin series between the electromotive actuator and the brake-applicationdevice; a control unit for controlling the wedge angle switching betweenthe tangential force absorption cylinder and the electromotive actuator;and a readjustment device for readjustment to compensate brake pad wear,wherein the readjustment device comprises an adjustable screw spindle,which is operatively connected to the brake-application device for thegenerating a follow-up movement of the at least one brake pad and iscoupleable to the electromotive actuator in order to be driven, and areadjustment piston, which is hydraulically adjustable in the tangentialforce absorption cylinder during a follow-up movement of the at leastone brake pad.
 2. The disc brake as claimed in claim 1, wherein areadjustment drive wheel forms, together with a shaft drive wheel whichis coupled to the screw spindle, a hydraulic gear motor which ishydraulically coupleable to the electromotive actuator via a hydraulicswitch.
 3. The disc brake as claimed in claim 1, wherein, in a case oftwo brake-application cylinders being used, the hydraulic gear motorcomprises a centrally positioned shaft drive wheel and two shaft drivewheels positioned at both sides, and further wherein said arrangementsimultaneously serves for synchronously adjusting the brake-applicationcylinders.
 4. The disc brake as claimed in claim 2, wherein thehydraulic switch is controllable by the control unit.
 5. The disc brakeas claimed in claim 1, wherein the readjustment piston is, for thefollow-up movement, connectable to the reservoir circuit via adirectional valve.
 6. The disc brake as claimed in claim 1, wherein theexpansion vessel of the reservoir circuit of the brake-internalhydraulic arrangement is equipped with a sensor for detecting pad wear,wherein the sensor is connected to a brake control unit which, for theactivation of the readjustment device for a corresponding follow-upmovement of the at least one brake pad, is coupled at least to theelectromotive actuator and to the control unit.
 7. The disc brake asclaimed in claim 1, wherein the control unit has a control disc which ishydraulically drivable, by way of a control drive in the form of ahydraulic gear motor, by the electromotive actuator via a switchingvalve.
 8. The disc brake as claimed in claim 1, wherein the readjustmentdevice comprises an emergency release device, which is coupled to thereadjustment drive wheel.
 9. The disc brake as claimed in claim 5,wherein the readjustment device has at least one sensor which detects areadjustment travel in order to determine a present follow-up movement,and transmits the readjustment travel to the brake control unit for theregulation of the readjustment device.
 10. The disc brake as claimed inclaim 6, wherein the readjustment device has at least one sensor whichdetects a readjustment travel in order to determine a present follow-upmovement, and transmits the readjustment travel to the brake controlunit for the regulation of the readjustment device.
 11. The disc brakeas claimed in claim 7, wherein the readjustment device has at least onesensor which detects a readjustment travel in order to determine apresent follow-up movement, and transmits the readjustment travel to thebrake control unit for the regulation of the readjustment device. 12.The disc brake as claimed in claim 1, wherein the sensor for determininga readjustment travel is a multi-turn potentiometer which is directly orindirectly coupled to the screw spindle.